Prof Arzhang Ardavan

Abstract:

Pyrrolidine derivatives of N@C60 have been synthesized and characterized. The photochemical stability of the derivatives as well as pristine N@C60 are studied and compared. While the attachment of a pyrrolidine group to C60 cage significantly lowers the photolytic stability of N@C60, the effect of a peripheral optically active pyrenyl group on photoinduced decay is negligible. A mechanism involving carbon-carbon bond dissociation and a subsequent inversion of the endohedral nitrogen atom is proposed to account for the observed spin loss. © 2011 Elsevier B.V. All rights reserved.

Abstract:

Electron spin qubits in molecular systems offer high reproducibility and the ability to self-assemble into larger architectures. However, interactions between neighboring qubits are "always on," and although the electron spin coherence times can be several hundred microseconds, these are still much shorter than typical times for nuclear spins. Here we implement an electron-nuclear hybrid scheme which uses coherent transfer between electron and nuclear spin degrees of freedom in order to both effectively turn on or off interqubit coupling mediated by dipolar interactions and benefit from the long nuclear spin decoherence times (T2n). We transfer qubit states between the electron and N15 nuclear spin in N15@C60 with a two-way process fidelity of 88%, using a series of tuned microwave and radio frequency pulses and measure a nuclear spin coherence lifetime of over 100 ms. © 2011 American Physical Society.

Abstract:

We describe a low-temperature sample probe for the electrical detection of magnetic resonance in a resonant W-band (94  GHz) microwave cavity. The advantages of this approach are demonstrated by experiments on silicon field-effect transistors. A comparison with conventional low-frequency measurements at X-band (9.7  GHz) on the same devices reveals an up to 100-fold enhancement of the signal intensity. In addition, resonance lines that are unresolved at X-band are clearly separated in the W-band measurements. Electrically detected magnetic resonance at high magnetic fields and high microwave frequencies is therefore a very sensitive technique for studying electron spins with an enhanced spectral resolution and sensitivity.

Abstract:

Competition between electron localization and delocalization in Mott insulators underpins the physics of strongly correlated electron systems. Photoexcitation, which redistributes charge, can control this many-body process on the ultrafast 1,2 timescale. So far, time-resolved studies have been carried out in solids in which other degrees of freedom, such as lattice, spin or orbital excitations 3-5 , dominate. However, the underlying quantum dynamics of bareg electronic excitations has remained out of reach. Quantum many-body dynamics are observed only in the controlled environment of optical lattices 6,7 where the dynamics are slower and lattice excitations are absent. By using nearly single-cycle near-infrared pulses, we have measured coherent electronic excitations in the organic salt ET-F 2 TCNQ, a prototypical one-dimensional Mott insulator. After photoexcitation, a new resonance appears, which oscillates at 25THz. Time-dependent simulations of the Mottg Hubbard Hamiltonian reproduce the oscillations, showing that electronic delocalization occurs through quantum interference between bound and ionized holong doublon pairs. © 2011 Macmillan Publishers Limited. All rights reserved.